This study focuses on the hydrodynamic interaction between two or three human swimmers in competitive swimming. Although the swimming performance of a single swimmer has been widely examined, studies on the interaction between multiple competitive swimmers are very rare. Experiments showed evidence that the drag of a swimmer could be modified by the existence of the other adjacent competitors (Chatard & Wilson. 2003 Med. Sci. Sports Exerc. 35, 1176–1181. (doi:10.1249/01.MSS.0000074564.06106.1F10.1249/01.MSS.0000074564.06106.1F)). The following questions arise: (1) what mechanism determines the interaction; (2) which position experiences drag reduction or drag increase; (3) how much can drag be reduced or increased in a formation? According to the authors' knowledge, such questions have not been addressed by any published literature. Therefore, the main purpose of this study is to find the mechanism of the hydrodynamic interaction between human swimmers and to quantify this interactive effect by using a steady potential flow solver. The free-surface effect was fully taken into account in our calculations. We firstly calculated the wave drag of a swimmer swimming solely in an open swimming pool. Then we calculated the wave drag of the same swimmer when he/she swam in the wake region of one or two leading swimmers. The results showed that the hydrodynamic interaction made a significant contribution to the drafter's wave drag. By following a leading swimmer, a drafter at wave-riding positions could save up to 63% of their wave drag at speed of 2.0 m s−1 and lateral separation of 2.0 m. Particularly, when a drafter is following two side-by-side leaders, the drag reduction could even be doubled. To the authors' knowledge, this study is the first to demonstrate that the hydrodynamic interaction between human swimmers can best be described and explained in terms of wave interference effect on the free water surface. When the wave cancellation effect is observed, the wave drag of a drafter could be minimized, and this wave cancellation effect can be achieved only when the drafter is in a wave-riding position.

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7A controller is usually used to maximize the energy absorption of wave energy converter. Despite the 8 development of various control strategies, the practical implementation of wave energy control is still 9 difficult since the control inputs are the future wave forces. In this work, the artificial intelligence 10 technique is adopted to tackle this problem. A multi-layer artificial neural network is developed and 11 trained by the deep machine learning algorithm to forecast the short-term wave forces. The model 12 predictive control strategy is used to implement real-time latching control action to a heaving point-13 absorber. Simulation results show that the average energy absorption is increased substantially with 14 the controller. Since the future wave forces are predicted, the controller is applicable to a full-scale 15 wave energy converter in practice. Further analysis indicates that the prediction error has a negative 16 effect on the control performance, leading to the reduction of energy absorption. 17 Keywords: wave energy converter; wave energy control; energy absorption; neural network; deep 18 machine learning; wave force prediction. 19 Henriques [6] presented a review on the oscillating-water-column WEC. Stansby et al. [7] examined 29 the dynamics of multi-float WEC concept M4. 30Although a set of WEC concepts have been developed, the energy harvesting efficiency is still not 31 satisfactory, especially in the off-resonance state. One of the solutions is the usage of a non-linear 32 power take-off (PTO) system. Zhang and Yang [8] showed that a PTO system with nonlinear spring 33 could harvest more energy in random waves. Xiao et al. [9] investigated the power capture of an 34Eq. (4) is a first-order, one-variable differential formula, which is easier to handle. Given the initial 112 condition x(0) = 0, it becomes a classical initial-value problem and the time series of floater 113

A new type of floating breakwater (FB) is proposed in this paper. Its hydrodynamic performance has been tested. The structure of the new breakwater named cylindrical floating breakwater (CFB) consists of two parts: a main body of rigid cylinders, and a flexible mesh cage containing a number of suspending balls that are intended to absorb the wave energy into their mechanical energy. A series of experiments were carried out on the new floating breakwater and traditional double pontoons and box floating breakwaters to compare their performances. A two-dimensional wave flume was used in the experiment; the incident and transmitted waves, the tensions on the mooring lines and the motion responses of the floating breakwaters were measured. Results showed that the new floating breakwater had a better performance than the traditional double pontoons and the box floating breakwaters: wave transmission was significantly reduced by the mesh cage with the balls, especially for long waves